This man decides to stick around during a confrontation while a third party tries to separate them; when the distance is closed, he is stabbed by an unseen knife.
This is the reality of many knife attacks – if someone really wants to stab someone, it makes no sense to brandish the knife and make the victim aware it exists. If they have any common sense, they will simply draw the knife once the distance is closed.
In this case, a major blood vessel in the abdomen was struck, and the man lost consciousness a short time later. When police are seen arriving the victim displays agonal breathing, which is a sign he is very close to death.
Agonal respiration, gasping respiration or agonal breathing is a distinct abnormal pattern of breathing and brainstem reflex characterized by gasping, labored breathing, accompanied by strange vocalizations and myoclonus. Possible causes include cerebral ischemia, extreme hypoxia (inadequate oxygen supply to tissue), or even anoxia (total depletion of oxygen). Agonal breathing is an extremely serious medical sign requiring immediate medical attention, as the condition generally progresses to complete apnea and heralds death. The duration of agonal respiration can be as brief as two breaths or last up to several hours.